


Transposition

by BlueMinuet



Category: Tennis no Oujisama | Prince of Tennis
Genre: Age Swap, Inui juice, M/M, mention of vomit
Language: English
Status: Completed
Published: 2017-05-31
Updated: 2017-05-31
Packaged: 2019-05-17 11:23:14
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,406
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14831351
Author URL: https://archiveofourown.org/users/BlueMinuet/pseuds/BlueMinuet
Summary: Momo reached out and smacked his arm. “Listen to me! I heard about this from the upperclassmen in all the other sports teams. Every few years there’s some generation of magical first years that join and eclipse all the second years. They snap up all the regulars spots, leaving the second years to rust on the bench. Is that what you want to happen to us?”“I think that’s an urban legend,” Kaidou muttered.AU where the years are switched around, and Inui is Kaidou's kouhai.





	Transposition

**Author's Note:**

  * For [Marks](https://archiveofourown.org/users/Marks/gifts).



> This was a bonus round fill for SASO 2017. The original post can be found [here](https://sportsanime.dreamwidth.org/21522.html?thread=10570770#cmt10570770).
> 
> And it only took me a whole year to crosspost it...

“I’m telling you, Viper, we have to be careful.” 

Kaidou hissed, not really listening. Typically, he prefered running to be a conversationless activity. Which, to be fair, was the same sentiment he held about nearly all activities, but the point remained. 

Momo reached out and smacked his arm. “Listen to me! I heard about this from the upperclassmen in all the other sports teams. Every few years there’s some generation of magical first years that join and eclipse all the second years. They snap up all the regulars spots, leaving the second years to rust on the bench. Is that what you want to happen to us?” 

“I think that’s an urban legend,” Kaidou muttered. 

There were a lot of first years that were joining the club, Kaidou had to admit that. They were eager and bright-eyed and ready to take on any challenge, but Kaidou figured that was every first year. Just because there were a lot of them didn’t mean anything. Sure, a few of them seemed to have some experience and interesting abilities, but that didn’t mean much. 

Kaidou caught sight of one of them running laps just ahead of them, though whether he was running faster than them or just lagging that much behind in overall laps, Kaidou wasn’t sure. He had a notebook tucked under his arm that he hadn’t dropped. Kaidou wondered if juggling that was slowing him down. 

Idiot. 

“It’s true!” Momo shouted in his ear. “Look, I don’t like you, and you don’t like me, but we have to stick together! We have to step up our game and make sure none of these little kids jump over us to the regular slots and make us look like chumps!” 

Kaidou grunted in reply. “They’re not little kids. They’re only one year younger.” 

“They’re _twelve_ , Viper,” he said. “We’re _thirteen_. It’s different.” 

Kaidou hissed again.  
  


* * *

  
Kaidou would have been perfectly content to let the first year thing drop altogether, but it seemed that his school problems couldn’t be so easily contained to the school campus. 

He was taking his evening jog cutting through the park, just past the street tennis courts when something caught his eye. He stopped, jogged backwards for a minute, and looked. 

He recognized the first year instantly, his dangerously jagged hair and sharp square glasses were distinctive enough. He was hitting against the backboard, still running himself ragged although the sun was nearly set. But that wasn’t all, there were also notebooks scattered all around him, hasty chicken scratch notes covering each of the white surfaces scattered around him. He seemed to easily move around them as he practiced, even though he was close to falling over in exhaustion. At least he had excellent awareness of his surroundings. 

He missed, his racket swinging against air as the ball whooshed past him. He didn’t slump in defeat or grumble in anger. Instead he stood stoically for a second, deep in thought. Kaidou almost thought to ask him about it — or at least check to be sure he hadn’t turned into a statue — when he finally moved, curling over one of his notebooks and scribbling furiously. 

Kaidou turned and jogged away without saying a word.  
  


* * *

  
“What’s the deal with that one?” 

The first year he was talking to nearly jumped out of his skin. Kaidou still wasn’t sure about all their names, and if he was being honest, he didn’t care all that much. This one seemed nice — a people person — so if any of them knew what he wanted to know it was this one. He thought his name was Oishi, or something like that. 

“Kaidou-senpai?” he asked, his brow knit on his forehead in something like fear or confusion. Maybe both. 

Kaidou nodded at the spiky-haired one, who was practicing on the court just ahead of them. “That one.” 

“Oh, that’s Inui,” Oishi said. “What did you want to know about him?” 

Kaidou stared down at the first year, dead silent. 

Oishi laughed nervously. “Umm, well, he kind of keeps to himself. Not that he isn’t nice… He is, sort of. Or, he’s trying. At least I think he’s trying.” He looked up at Kaidou, as if checking to see if he had fulfilled Kaidou’s curiosity, but finding the same stern look glowering down at him, he continued. “He was a really good doubles player back in elementary school, or so I hear. But he doesn’t want to play doubles anymore. He keeps going on about wanting to get better and be the best in our year.” 

Kaidou grunted in acknowledgement, and Oishi sighed slightly, perhaps relieved to have been useful. 

“Is that what’s up with all the notebooks?” 

“I think so,” Oishi said with a shrug. “Or, at least some of them… There’s also, well…” 

Kaidou arched an eyebrow. “What?” 

Oishi shrugged, looking away. “I wouldn’t drink anything he gives you, is all I’m saying.” 

Kaidou hissed. Oishi seemed to want to say something else, but Kaidou walked off, unconcerned.  
  


* * *

  
“You won’t get any better like this.” 

Kaidou watched his kouhai’s body tense. He was panting, hands and knees on the clay of the court, while the ball that had escaped his reach rolled idly backwards. Kaidou stopped it with his foot before it rolled over one of Inui’s many notebooks. 

“What do you mean?” Inui asked, between swallowing gulps of breath. 

“You’re going to hurt yourself,” Kaidou said. “You’re just a kid.” 

Inui pushed himself up, sitting on his heels. His chest was still heaving, but his breath was slowly evening out. He straightened his glasses. “Technically, you’re still growing too, senpai.” 

Kaidou hissed. 

They fell silent for a minute. Inui was looking at him, and Kaidou got the impression of eyes sweeping over him, assessing. 

“Why don’t you want to play doubles anymore?” Kaidou asked. 

Inui’s head turned away so fast, Kaidou expected to hear his neck snap. He looked resolutely away, and said nothing. 

Kaidou rolled the ball back towards him, and left him in peace.  
  


* * *

  
“I made a training menu for you.” 

Kaidou looked up. He’d been stretching on the grass, enjoying the solitude, and hadn’t noticed anyone walking up. Apparently, Inui was stealthy in addition to all of his other odd qualities. 

It was strange, looking up at his kouhai from this angle. He was all rough angles that were just lightly padded with softness, like a puppy that hadn’t lost all its baby fur, some strange halfway point to a final form that hadn’t quite taken shape yet. 

“You did what?” Kaidou asked. 

Inui was holding out a folded piece of paper to him. Kaidou took it gently. He thought about what Oishi had said of Inui; nice, but keeps to himself. This didn’t seem to fit the second point. 

“It takes into account your physique, your level of skill, and it should intensify as you try to reach your goal.” 

Kaidou stared at him. “Goal?” 

“You don’t want the first years to surpass you,” Inui said evenly. “This will keep you one step ahead.” 

Kaidou arched an eyebrow. “You’re helping me stay better than you?” 

Inui shook his head. “The odds of me making the regulars this year is less than 5%. I’m not the first year you need to beat.” 

Before Kaidou could say anything else, Inui was already walking away.  
  


* * *

  
“What part of our pact did you not understand, Viper?” 

Kaidou didn’t say anything, just kept running, trying to focus on not falling behind in laps. Unfortunately for him, Momo was, as ever, persistent. 

“What happened to you and me against the first years?” Momo whined. 

“We’re all on the same team,” Kaidou muttered. 

“We are not!” Momo shouted. “It’s eat or be eaten, Viper. We don’t have time for you to be fraternizing with your little first year toy.” 

Kaidou pushed himself to put a gap between himself and Momoshiro. 

“Hey! Don’t run away when I’m talking to you!”  
  


* * *

  
Inui was kind of small, but he could run fast. 

Though, _small_ wasn’t quite the right word either. He was gangly, but hadn’t hit his growth spurt yet. Kaidou kind of dreaded what he might look like once he did. Would he end up taller than Kaidou by the time they were in high school? 

Kaidou shook his head. He barely knew the kid, and yet he was imagining a future of them at the same high school? He tried to get his thoughts together. 

Normally, running cleared his head enough, but somehow with Inui by his side, all sorts of thoughts popped up. Ever since he had started the training menu that Inui had given him, they’d been running and exercising together. Or, as much as they could; Inui had a much lighter training menu that he’d written for himself, though Kaidou somewhat wondered if that was simply to appease his own worry. 

When had he started worrying over first years? 

They came to a stop in the park, behind a bench not far from the street tennis courts. Kaidou flopped down on the grass, soaking in the coolness of the leaves. He let his eyes drift closed for a minute, and when he opened them Inui was hovering over him. 

Kaidou was no longer startled by the strange looming of his kouhai. 

Inui settled down next to him, pulling off the light backpack he’d brought with him. He fished around inside for a minute before producing a sports bottle from the depths of it. He turned to Kaidou, and though Kaidou couldn’t be sure, he thought he sensed a bit of nervousness. 

“What’s that?” Kaidou asked. He hoped the answer would be ‘water’ but somehow, in his heart, he knew the answer wasn’t that simple. 

“It’s, um…” Inui faltered, and Kaidou’s eyes widened, unused to this kind of hesitance. “I’ve been dabbling in making recovery drinks,” Inui finally managed to say, with some fidgeting. “Most people seem to have… adverse reactions, but as far as nutritional value, it can’t be matched.” He squirmed a bit, uncharacteristically. This meant a lot to him, Kaidou realized in a flash. “Would you like to try it?”

Kaidou sat up, and couldn’t do anything but nod. 

The thousand watt smile Inui gave him at that made him want to drink gallons of the stuff.  
  


* * *

  
It was only much later that Kaidou remembered the rest of Oishi’s advice. 

_“I wouldn’t drink anything he gives you, is all I’m saying.”_

He’d managed to drink the whole bottle and smile, and at least he hadn’t vomited until after Inui was out of line of sight. 

The first time he vomited… The first of many times, Kaidou was coming to realize. 

He curled up on his bathroom floor, and thought of Inui’s smile.  
  


* * *

  
“I’m not sure if it will work,” Inui said, leading Kaidou down an embankment and towards the canal. “But I think water resistance will give you the edge you need to perfect your shot.” 

Kaidou was coming to learn that _”I’m not sure if it will work.”_ was actually code for _”The percentage it will work is at least over 80% but all the senpais keep telling me to stop quoting numbers at them.”_

Kaidou didn’t really mind the numbers, truth be told, but instead he just nodded. 

Inui sat down at the water’s edge, pulling off his shoes and rolling up his pants. Kaidou hadn’t realized he was going to have company in the canal, but he wasn’t about to complain. He didn’t get right down to preparing, and instead just watched Inui. He was so much more animated when it was just the two of them. He’d caught some of the other members of the team calling Inui a robot, but Kaidou was coming to realize that, while that wasn’t necessarily wrong, there were deeper layers beyond his mechanical shell. 

Inui glanced over at Kaidou’s shoes, then up and up and up until he was staring at his face. “Kaidou-senpai? Aren’t you going to try my training?” 

Kaidou hissed. “Sure. But on one condition.” 

Inui raised an eyebrow. Kaidou hadn’t seen him do that much before and wondered if his mannerisms were rubbing off. “What is it?” Inui asked. 

“Once I’ve perfected the shot here, try it out with me,” Kaidou said. 

Inui stared at him. “Do you… mean…”

“In doubles,” Kaidou said, leaving no ambiguity. 

Inui looked away. His movements were stiffening too, as if the metallic shell was clamping back around him. “I… I don’t play doubles.” 

“The boomerang can’t make it into singles court,” Kaidou said. “Not yet anyway.” He stared down at Inui. “I need someone to help me play it until I can.” 

Inui turned back to him. “But I can’t…” 

“No one else can help me,” Kaidou said. “No one else has… trained this close with me.” 

“I’d hold you back,” Inui said. “I’m not the best first year, and…” 

Kaidou hissed. “Then you should jump at the chance to play with your senpai. None of the other first years will get to.” 

Inui straightened up a little, his brain seeming to crunch those numbers a bit.

Kaidou sat down, starting to undo his laces. Silence passed over them, but it was an easy one, Kaidou giving Inui the time he needed. 

Inui shrugged his backpack off, and pulled his notebook out from it. “I’ll need to collect more data on your shot to work with you better.” 

Kaidou nodded, and slipped into the water.  
  


* * *

  
When the new school year came, Kaidou was a bit perturbed that Inui was no longer looking up to him. In the physical sense. They were nearly eye to eye after his growth spurt, and Kaidou just knew that next year he’d have to look up at his towering kouhai. 

Inui was grabbing his racket from his bag. A few bottles of newly improved Inui Juice 2.0 fell out as well, sloshing on the floor, but unfortunately not spilling. Kaidou said nothing as Inui gathered them up and packed them back up in his locker. 

“Ready for the new year, senpai?” 

Kaidou smirked a little. “We’ll have to work hard if we’re going to show your classmates who the better doubles pair is.” 

Inui pushed his glasses up. “Don’t worry. I’ve been collecting data on Eiji and Oishi for more than a year. I know exactly what we need to do.” 

When Kaidou looked back at him, Inui was smiling. 

“Then let’s do it.”


End file.
